Influenza Picking Up in U.S., Predominantly A(H3N2)

Last Updated: December 08, 2017.
Influenza activity was low during October 2017 but started increasing in November, with influenza A, predominantly A(H3N2), most commonly identified, according to research published in the Dec. 8 issue of the U.S. Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Influenza activity was low during October 2017, has been increasing since the start of November

FRIDAY, Dec. 8, 2017 (HealthDay News) -- Influenza activity was low during October 2017 but started increasing in November, with influenza A, predominantly A(H3N2), most commonly identified, according to research published in the Dec. 8 issue of the U.S. Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Vivien G. Dugan, Ph.D., from the CDC in Atlanta, and colleagues summarized U.S. influenza activity during Oct.1 to Nov. 25, 2017.

The researchers note that influenza activity was low during October 2017 in the United States, but since the start of November, activity has been increasing. The most commonly identified viruses have been influenza A viruses, with influenza A(H3N2) predominating. Several indicators of influenza activity were reported to be higher than normally seen at this time of year. Most influenza viruses characterized during this period were genetically or antigenically similar to the Northern Hemisphere cell-grown vaccine reference viruses for 2017 to 2018. Currently circulating viruses seem not to have undergone significant antigenic drift; circulating A(H3N2) viruses are antigenically less similar to egg-grown A(H3N2) viruses used for most U.S. influenza vaccine production. Hospitalizations and deaths were more common and vaccine effectiveness was lower in recent past seasons in which A(H3N2) viruses predominated; it is unclear which influenza viruses will predominate in the 2017 to 2018 season.

"Vaccination should continue to be offered as long as influenza viruses are circulating and unexpired vaccine is available," the authors write.

One author disclosed holding two patents relating to influenza vaccines.